# File lib/phusion_passenger/utils.rb, line 857
        def backtrace_string(current_location = nil)
                if current_location.nil?
                        location = nil
                else
                        location = "in #{current_location} "
                end
                return "*** Exception #{self.class} #{location}" <<
                        "(#{self}) (process #{$$}, thread #{Thread.current}):\n" <<
                        "\tfrom " << backtrace.join("\n\tfrom ")
        end